Why is adding a root tag around the data (which is not XML BTW, as it does not parse) not an option? You could use a pipe or create a temp file to hold the real XML.:

open( XML, qq{echo "<doc>" cat $file echo "</doc>" |})
or die "could not open file: $!";
$p->parse( \*XML);
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BTW, XML::Parser is not a SAX parser, see XML::SAX::Intro for more details.